BME280 Schematic

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RedIron
 
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BME280 Schematic

Post by RedIron »

Hi everyone,

I would like to make a custom PCB with a BME280 chip on it.
I've looked at the schematic that adafruit provides for its breakout board and there's one thing I do not understand the purpose of.

Top left are 2 level shifter used for SDA and SCL lines form the BME280 to the Arduino Pro Mini in my case.
Top right is the voltage regulator 5v to 3.3v.
Bottom left the chip itself and how to connect it.

But what it the purpose of top middle part (where the 1n4148 diode is) ? Is it necessary ?

Thanks for you help.
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Adafruit BME280 Schematic.png
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adafruit_support_bill
 
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Re: BME280 Schematic

Post by adafruit_support_bill »

For SPI communication. the CS is pulled LOW to select the device for communication. The chip itself runs at 3.3v and has internal pullups for the CS pin. (see p.33 of the datasheet: https://cdn-shop.adafruit.com/datasheet ... 001-10.pdf )

The diode allows a 5v processor to pull the pin LOW, but blocks it from pulling it HIGH to 5v.

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RedIron
 
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Re: BME280 Schematic

Post by RedIron »

Thanks for you answer.

I intend to use I2C, is it therefore necessary ?

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adafruit_support_bill
 
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Re: BME280 Schematic

Post by adafruit_support_bill »

Sections 6 and 7 discuss the role of the CSB pin in i2c communication. Figure 17 shows the recommended connections for i2c.

https://cdn-shop.adafruit.com/datasheet ... 001-10.pdf

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RedIron
 
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Re: BME280 Schematic

Post by RedIron »

Ok thanks for the advise, I will do as shown in figure 17.

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